In the operation of crawler type vehicles, it is often desirable to assure that priority is given to the operation of selected work elements of a plurality of work elements. For example, it may be important that first and second track motors are assured of receiving sufficient fluid to satisfy their maximum fluid demand capacity even at the expense of not being able to supply the hydraulic fluid necessary to satisfy the demands of other work elements of the hydraulic system. An example where such a priority system would be important is in operating an excavator in extremely rugged terrain where it is desirable to always have full power available to operate the track motors.
Further, it is desirable that a priority system such as this be constructed to function from one or a plurality of pumps and the pump or pumps be controlled by a single control valve in response to the operating pressures of the plurality of working elements. It is also advantageous to control the maximum pressure subjected on each working element in order to reduce waste of energy and material.
This invention therefore resides in a controlled priority fluid system of a crawler type vehicle.